A 15 year service life on any battery is outstanding! Desulfators... don't waste your money. If you can do simple regular maintenance to a free flooded/conventional battery it's still the best bang for the buck. If you are less likely to maintain/service your battery and money isn't a concern AGM is a good option and contrary to popular opinion, does not need modification to your charging system. Just don't leave your car for any length of time with even a small load because it will drain the AGM to 0 volts.